gpu.c: compute_group_tilings: take ppcg_kernel instead of gpu_gen
gpu.c: compute_group_tilings: take ppcg_kernel instead of gpu_gen

This function only depends on the kernel, so there is no need to pass
along the gpu_gen.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

nicolasvasilache/ppcg,Meinersbur/ppcg,Meinersbur/ppcg,nicolasvasilache/ppcg